FIG. 8 is a circuit diagram showing the construction of a power converter of related art disclosed in for example U.S. Pat. No. 5,646,511. In this power converter, a series transformer having its primary winding connected in series with a power line, a distribution line or a single-phase AC wire for an electric train or the like (hereinafter abbreviated to ‘line’) and multiple array transformers on the secondary side of this series transformer are combined in two stages to connect AC-DC converter units to the line. This power converter has the function of a line power tide current control apparatus. In the figure, the primary winding 201 of a series transformer 200 is connected between the power supply side 1 of a line and a power supply side or load side 2 of the line. The primary windings 411 to 441 of array transformers 410 to 440 (the case of a four-stage array is shown) are connected in series with the secondary winding 202 of the series transformer 200. The AC sides of AC-DC converter units 510 to 540 are respectively connected to the secondary windings 412 to 442 of the array transformers 410 to 440, and the DC sides of the four AC-DC converter units 510 to 540 are connected to a common DC circuit 511.
Because power converters of related art have been constructed like this, if even one of the multiple AC-DC converter units 510 to 540 fails, because it is impossible to maintain the DC voltage of the DC circuit 511, none of the AC-DC converter units can be operated, and it has been necessary to shut down the power converter. And there has been the problem that the power converter has to be shut down until repair or periodic checking is complete, and the availability of the system falls.
The present invention was made to solve these problems, and it is an object of the invention to provide a power converter capable of continuing to operate as a system even when one of multiple AC-DC converter units fails or is stopped for a periodic check.